<template>
  <ul class="list">
  	<li  class="item" v-for="item of letters" :key="item" :ref="item" 
  		@click="handleLetterClick"
  		@touchstart="handleTouchStart"
  		@touchmove="handleTouchMove"
  		@touchend="handleTouchEnd"
  		>{{item}}</li> 	
  </ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props:{
		cities: Object
	},
	computed: {
		letters () {
			const letters=[]
			for(let i in this.cities){
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated (){
		this.startY=this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e){			
			this.$emit('change',e.target.innerText)		
		},
		handleTouchStart () {
			this.touchStatus=true
		},
		handleTouchMove (e) {
			if(this.touchStatus){	
				if(this.timer){
					clearTimeout(this.timer)
				}
				this.timer= setTimeout(()=>{
					const touchY=e.touches[0].clientY-79
					const index=Math.floor((touchY-this.startY)/20)
					if(index >= 0 && index < this.letters.length){
					this.$emit('change',this.letters[index])
				  }
				},16)															
			}
		},
		handleTouchEnd () {
			this.touchStatus=false
		}
	}
}
</script>

<style lang="stylus" scoped>
@import '~@/assets/styles/varibles.styl'
  .list
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    background: #eee 
    display: flex
    flex-direction: column
    justify-content: center
    .item
      text-align: center
      line-height: .4rem
      color: $bgColor 
</style>